The signing of the Anglo-Irish Treaty by the Irish delegation in London caused an angry reaction among the less compromising elements in Sinn Féin and among a majority of the IRA. Dáil Éireann ratified the Treaty by 64 votes to 57 after a lengthy and acrimonious debate, following which President Éamon de Valera resigned. Sinn Féin split between pro-Treaty and anti-Treaty factions, and the Army did likewise. The majority of headquarters staff, many of whom were close to Michael Collins, supported the Treaty, but opinion among IRA volunteers was divided. By and large, IRA units in Munster and most of Connacht were opposed to the Treaty, while those in favour predominated in the Midlands, Leinster and Ulster. The pro-Treaty volunteers formed the nucleus of the new National Army.

Anti-Treaty officers called an army convention in March 1922, attended by their supporters, which reaffirmed their opposition to the Treaty. They repudiated the authority of the Dáil, claiming that its members had broken their oath to defend the Irish Republic, and declared their own Army Executive to be the real government of the country until the Republic was formally established. The reasons why volunteers chose pro- and anti-Treaty positions are complex. One factor was an evaluation of the military situation. Whereas Collins, Richard Mulcahy and Eoin O'Duffy felt that the IRA could not continue to fight the British successfully, anti-Treaty officers such as Ernie O'Malley and Tom Barry felt that the IRA's position was stronger than it had ever been. Another factor was the role of powerful personalities; where the leader of an IRA unit—for example Sean McEoin, who sided with the Treaty in County Longford—took sides, often the remainder of his command joined him. The same was also true for anti-Treaty leaders such as Liam Lynch in Cork.

On the outbreak of civil war in June 1922, the government of the Irish Free State issued directives to newspapers that its Army was to be called "The National Army", and that its opponents were to be called "Irregulars" and were not to be associated with the IRA of 1919–1921.[5] This attitude hardened as the Civil War went on, and especially after the killing of Michael Collins in an ambush in August 1922. Collins wrote to W. T. Cosgrave on 25 July 1922 that those on the anti-Treaty side were "misguided, but practically all of them are sincere". However, the subsequent government attitude under Cosgrave was that the anti-Treaty side were rebels against the lawful government, and were not entitled to recognition as legitimate combatants. Some of the officers of the new Irish Army, led by Liam Tobin, formed an association called the "Old IRA" to distinguish themselves from the anti-Treaty fighters. Some pro-Treaty IRA officers, such as Eoin O'Duffy, alleged that the "Irregulars" had not fought the British in the War of Independence. O'Duffy claimed that the Kerry IRA's sole contribution in 1919–21 was "the shooting of an unfortunate soldier on the day of the truce". In Kerry's case (which saw more Royal Irish Constabulary (RIC) men killed than anywhere else outside Dublin and Tipperary),[citation needed] this was far from true; however, some areas such as County Sligo and County Wexford did see considerably more action in the Civil War than in the War of Independence. Other IRA men such as Florence O'Donoghue formed a group called the "neutral IRA", which tried to reconcile the two factions.

Meanwhile, the IRA in Northern Ireland maintained its links with Michael Collins; the only Northern IRA leader to join the anti-Treaty side was Belfast commander Joe McKelvey. The Northern IRA launched a renewed military offensive in May 1922, in which it was aided covertly by both the National Army and the anti-Treaty IRA.[citation needed] This was interrupted by the outbreak of civil war in the new Irish Free State. Many Northern IRA men then had to flee the North in order to escape internment or worse at the hands of the Northern authorities. Over 500 of them ended up in the National Army during the civil war.

The IRA had been expanded hugely in 1922, from perhaps 15,000 men before the truce with the British in July 1921, to over 72,000 by November 1922. Veterans of the War of Independence derisively termed the new recruits "truceileers". These were to divide in broadly the same ratio as the veterans; however, most of them did not take part in the Civil War.[citation needed] At the beginning of the Civil War, the Free State had about 8,000 fighters, mostly pro-Treaty IRA volunteers. The anti-Treaty side could muster about 15,000 men but it could not arm them all. At the start of the war, they had just under 7,000 rifles, a few machine guns and a handful of armoured cars taken from British garrisons (who were under orders not to fire on IRA units) as they evacuated the country. The remainder of anti-Treaty IRA arms were shotguns (3,000 of which were confiscated after the Civil War) and other civilian weapons.[citation needed]

Public support for the Treaty settlement and the new Irish Free State was reflected in the victory of the pro-Treaty side in general elections in 1922 and 1923. Anti-Treaty forces controversially seized a number of public buildings in Dublin in April 1922, most notably the Four Courts. Eventually, after two months and under British pressure, Michael Collins decided to remove them by force. Pro-Treaty forces bombarded the building, which surrendered after two days. Confused fighting raged for another five days, with anti-Treaty elements of the IRA's Dublin Brigade, under Oscar Traynor, occupying O'Connell Street until they were dislodged by artillery fire.

In July 1922, the anti-Treaty IRA units held most of the south and west of Ireland. However the Republicans, under a new Chief of Staff, Liam Lynch, soon lost most of the territory they initially controlled. While the anti-Treaty side had a numerical advantage at the very start of the war, they were soon both outnumbered and outgunned. The Free State's National Army was quickly expanded to over 38,000 by the end of 1922 and to 55,000 men and 3,000 officers by the end of the war; one of its sources of recruits was Irish ex-servicemen from the British Army. Additionally, the British met its requests for arms, ammunition, armoured cars, artillery and aeroplanes. By August 1922, the Free State had re-taken all the major towns and territory held by republicans. The Free State's best troops were the Dublin Guard: a unit composed of former IRA men, mostly from the Dublin Brigade's active service unit who were to the forefront in the Free State's offensive of July–August 1922. They sided with the Free State primarily out of personal loyalty to Collins.

The anti-Treaty IRA was not equipped or trained to fight conventional warfare. Despite some determined resistance to the Free State advance south of Limerick by late August, most of them had dispersed to fight a guerrilla campaign.

The anti-Treaty guerrilla campaign was spasmodic and ineffective. Much of it was composed of the destruction of infrastructure such as the main railway bridge linking Cork with Dublin. They also burned many public buildings and "commandeered" supplies by force, alienating many civilians. Furthermore, without the public support that had existed during the War of Independence and facing an enemy who knew them and the countryside intimately, the anti-Treaty forces found that they could not sustain a guerrilla war such as that fought against Britain. Only in County Kerry was a relatively effective campaign fought, with the IRA units re-taking Kenmare and other towns from the Free State on several occasions. The IRA's relative popularity in this area had much to do with the brutality of the occupying Free State troops.[citation needed] Other areas of guerrilla activity included County Cork, western County Mayo, County Wexford and several other localities.

Despite the limitations of the anti-Treaty IRA's campaign, they still inflicted more fatalities on Free State troops (about 800) in the nine-month civil war than they had on British Crown forces, who lost about 600 killed in the almost three-year-long War of Independence (1919–1921). The disparity is no doubt due to the Free State troops' relative paucity of training and equipment compared with British forces.

Memorial to anti-Treaty insurgents executed by Free State forces at Ballyseedy, County Kerry, designed by Yann Goulet.

The conduct of the Civil War resulted in long-lasting bitterness on both sides. In September special emergency legislation came into effect under which military tribunals were empowered to pass death sentences. The head of the anti-Treaty forces, Liam Lynch, responded with an announcement that Free State TDs and Senators who had voted for the legislation would be targeted. A number of members of the Oireachtas were attacked, TD Sean Hales was killed and the property of parliamentarians burnt. In addition IRA men around the country burned many of the stately homes of the old Protestant Anglo-Irish landed class—a policy motivated by both class antagonism and nationalist resentment against a class traditionally seen as "pro-British". The Free State Government, for its part, officially executed 77 anti-Treaty prisoners. Government forces also carried out a number of atrocities against prisoners. This was particularly pronounced in Kerry, where the fighting was most bitter. On at least three occasions in March 1923, IRA prisoners were massacred with land mines in reprisal for the killing of Free State soldiers.[citation needed] Ironically, the men accused of these war crimes were mostly from the Dublin Guard, themselves IRA veterans from 1919–21. See also: Executions during the Irish Civil War

By 1923, the defeat of the anti-Treaty IRA seemed assured. It controlled no territory and its guerrilla campaign had little public support. The civil war petered out in mid-1923 after the death in action of IRA chief-of-staff Liam Lynch. Shortly afterward, on 24 May 1923, the anti-Treaty forces received an order, issued by Frank Aiken, their chief-of-staff, to "dump arms". Éamon de Valera supported this in his speech "Legion of the Rearguard":[6]

In de Valera's words, "Further sacrifice of life would now be vain and continuance of the struggle in arms unwise in the national interest and prejudicial to the future of our cause. Military victory must be allowed to rest for the moment with those who have destroyed the Republic. Other means must be sought to safeguard the nation's right."[7]

By this time, thousands of republicans were already prisoners of the Free State government led by W. T. Cosgrave; many more were arrested after they dumped arms and returned to civilian life. By late 1923, over 12,000 anti-Treaty IRA men were interned. The prisoners were released over the following year, with Éamon de Valera the last to leave Kilmainham Gaol in 1924.

In 1924 the IRA counted 14,500 members in total, including young men aged from 19 upwards, but with just over 5,000 weapons in its dumps. By 1926 the number of members had shrunk to 5,042. By 1930 the IRA possessed fewer than 2,000 members and only 859 rifles, indicating the decline in its military potential. The casualties of the anti-Treaty IRA in the Civil War have never been accurately counted, but are thought to have been considerably more than the 800 or so deaths suffered by the Free State Army, perhaps two or three times as numerous. Significantly however, the war had not been brought to an end by any kind of agreement between the two sides. The IRA of the post-Civil War era would never accept the Free State as a legitimate Irish government and would continue to oppose its existence.

In 1926, after failing to persuade Sinn Féin to participate in the political institutions of the Free State, de Valera formed a new political party, called Fianna Fáil, and many Sinn Féin members left to support him. De Valera would in 1932 become President of the Executive Council, at the head of the first Fianna Fáil government.

The IRA considered itself to be upholding the Republic that was declared in the 1916 Proclamation, and held that the government of the Irish Free State was illegitimate. It maintained that it remained the army of that Republic, in direct continuity with the IRA of the War of Independence period. There were several competing organisations on the radical republican side of Irish politics during this period. In addition to the IRA, these included the hard-line elements of anti-Treaty Sinn Féin, such as Mary MacSwiney, who had not followed de Valera into constitutional politics, and the rump of the anti-Treaty members of the Second Dáil, still proclaiming themselves the only legitimate Irish parliament. For most of this period, the IRA's relations with Sinn Féin were poor (IRA members were even forbidden to join the party), despite the reconciliation attempt represented by the 1929 Comhairle na Poblachta. In December 1938, a reconciliation finally took place between the IRA and the rump of the Second Dáil.

Before the republican Fianna Fáil party took power after winning the 1932 general election, many republicans viewed the Free State, with its censorship of newspapers and extensive coercive legislation, as a sham democracy, in the service of British imperialism. The IRA remained prepared to take over the country by insurrection, after which it expected to have to fight the British again. In November 1926 it seized 11 Garda Síochána barracks, shooting dead two Gardaí. The Free State immediately used its Special Powers Act to intern 110 IRA men the next day. IRA men assassinated Free State minister Kevin O'Higgins in 1927 in revenge for his perceived responsibility for executions in the Civil War. A total of four Gardaí were killed by the IRA in the period 1926–1936.[citation needed] In 1932 Gardaí shot dead two IRA leaders, George Gilmore and Thomas Ryan, in Kilrush, County Clare.[8]

When de Valera's Fianna Fáil party won the 1932 election, the IRA expected the Free State party Cumann na nGaedheal not to respect the result and prepared for another civil war. To their surprise, Cosgrave's party peacefully gave up power and instructed the police and armed forces to obey the new government.

In the first two years of Fianna Fáil government, the IRA's membership grew from a low of 1,800 to over 10,000. This can be put down to the radicalising impact of the Great Depression on the population, to which the IRA's new social radicalism (see next section) appealed. Another important factor was the formation of the Blueshirts: a quasi-fascist organisation set up by Eoin O'Duffy, originally composed of Civil war veterans of the Free State Army. The IRA and the Blueshirts both attacked political meetings and also fought street brawls against each other. While most of the fighting was conducted with fists or boots, at least one Blueshirt and one IRA man were shot dead in these clashes. IRA leaders saw in these events the beginnings of a republican revolution and the overthrow of the Free State. They were to be disappointed.

Initially, de Valera's Fianna Fáil government was friendly towards the IRA, legalising the organisation and freeing all their prisoners who had been interned by Cumann na nGaedhael. This afforded the IRA a quasi-legal status that meant Gardaí were unwilling to act against them for fear of repercussions. On his victory tour, de Valera snubbed a Garda guard of honour in Skibbereen, but saluted the IRA one.[9] By 1935 this relationship had turned to enmity on both sides. The IRA accused Fianna Fáil of "selling out" by not declaring a republic and by tolerating the continued partition of Ireland. De Valera banned the IRA in 1936, after they murdered a landlord's agent, Richard More O'Farrell, in a land dispute and fired shots at police during a strike of Dublin tramways workers, on top of their bank robberies. However, most of the IRA's republican constituency were reconciled to the Free State by de Valera's government, which introduced a republican constitution in 1937, abolishing the Oath of Allegiance to the British monarchy and introducing an elected president as head of state. The document also included a territorial claim to Northern Ireland. By the late 1930s at the latest, most Irish people disagreed with the residual Irish Republican Army's claims that it remained the legitimate 'army of the Republic'.

In Northern Ireland, the IRA's main role was to try to defend the Catholic community during outbreaks of sectarian rioting. For this reason Peadar O'Donnell, a left-wing IRA leader who was opposed to the Catholic nationalism of many IRA members, said disparagingly that "we don't have an IRA battalion in Belfast, we have a battalion of armed Catholics".

Twomey was not an ideological Marxist-Leninist (although there were some communists in the IRA at this time, such as Peadar O'Donnell); he saw the arrangement as purely utilitarian and regarded the Soviets as "shifty" and "out to exploit us."[10] Some republicans argued that they had lost the Civil War because they had not appealed to the social unrest in the country and had lacked any social or economic programme, which allowed communists to gain influence. Nevertheless, the IRA passed specifications of British "submarine detection sonar and aeroplane engines for bombers, military journals and manuals, and gas masks" to the Soviets[10] and the IRA's man in the U.S., "Mr. Jones", passed "reports of the army’s chemical weapons service, state-of-the-art gas masks, machine-gun and aeroplane engine specifications, and reports from the navy, air service and army" to Red Army intelligence.[10]

The IRA intervened in a number of strikes during this period, and IRA members campaigned against the payment of land annuities (in respect of the buying-out of landlords by the former British administration), with Peadar O'Donnell establishing the Anti-Tribute League in 1928. Many Communist Party of Ireland members were also members of the IRA at this time. Political initiatives such as Saor Éire, begun in 1931, were promoted by left-wing IRA members such as George Gilmore, Peadar O'Donnell and Frank Ryan. IRA members also helped establish the "Friends of Soviet Russia", from which they later expelled Communist Party members when relations between the two organisations deteriorated.

This burst of what has sometimes been termed "social republicanism" expired in the mid-1930s. In 1931 Saor Éire had quickly collapsed due to the combination of fierce reaction from the Catholic Church, deeply hostile to anything that appeared communist, and repressive legislation immediately introduced by the government. Left-wing IRA members, including Peadar O'Donnell, Frank Ryan and George Gilmore, frustrated with the failure of the IRA to achieve either "The Republic" or socialist revolution, left in 1934 to set up a new party, the Republican Congress. This in turn was ultimately a failure, partly because Twomey and other conservative elements in the IRA leadership opposed it and forced its supporters to leave the organisation. The Congress itself also split and collapsed after its first general meeting in 1935. From the debacle of the Republican Congress until it took a leftward turn again in the 1960s, the IRA would be inspired primarily by a conservative, strictly nationalist political outlook.

In 1936–37, a number of ex-IRA men were among the Irish fighters (later to become known as the Connolly Column) who joined the largely socialist International Brigades to fight for the Second Spanish Republic against the Nationalists during the Spanish Civil War. The IRA did not show any support for the Spanish Republic and subsequently banned members for joining the Connolly Column.[11] Frank Ryan was perhaps the most prominent Irish participant. (At the same time, IRA opponent and Greenshirts leader Eoin O'Duffy organised the Irish Brigade to go to Spain to fight on the opposing side, with Francisco Franco's Nationalists.)

In 1932 Fianna Fáil under de Valera formed its first government in the Irish Free State, and republican prisoners were released and the organisation unbanned. Confrontations between the IRA and the Blueshirts were a feature of political life in the early 1930s, with the former breaking up political meetings of Cumann na nGaedheal under the slogan "no free speech for traitors" and accusing the latter of being fascists.

The IRA was banned once again in 1935, as were the Blueshirts. Moss Twomey was imprisoned, and was succeeded as chief of staff by Seán MacBride. De Valera's government increasingly followed a strict anti-IRA policy. In 1936 Vice-Admiral Henry Somerville was assassinated in his West Cork home by IRA gunmen for recruiting many local Irishmen, including IRA members and even a captain in the Drimoleague IRA company, into the British military which combined with other members immigrating to the UK for work had a notable effect on IRA manpower. The Gardaí described the assassination as "a well and coolly thought-out outrage, well-planned and daringly executed”. Seán Russell became chief of staff in 1938, and set about preparations for a bombing campaign against Britain. In January 1939, the IRA Army Council declared war against Britain, and the Sabotage Campaign began a few days later.

On 23 December 1939, IRA members stole almost the entire reserve ammunition store of the Irish Army from the Magazine Fort in Dublin's Phoenix Park. This became known as the "Christmas Raid" in IRA folklore. The Royal Ulster Constabulary (RUC) found two and a half tons of the stolen ammunition inside County Armagh on 2 January 1940. The next day the Irish Minister for Justice, Gerald Boland, at an emergency session of the Dáil, introduced the Emergency Powers Bill to reinstate internment, Military Tribunal, and executions for IRA members. It was rushed through and given its third reading the next day creating the Emergency Powers Act. It was later used to execute at least six IRA volunteers in Ireland between 1940 and 1944.[12] Peter Barnes and James McCormack who had been arrested in England shortly following an IRA bomb that exploded in Coventry on 25 August 1939 resulting in the deaths of several uninvolved English civilians, were executed on 7 February 1940. Republican publication An Phoblacht did not deny their mission in England and IRA membership, but maintains that they were not involved with the Coventry bombing.

By 1941, the IRA numbered fewer than 1,000 members, many of whom were imprisoned. Most of its able political organisers had left in the mid- to late-1930s and its "natural constituency" had been appropriated by Fianna Fáil.

During the Second World War, the IRA hoped for support from Germany to strike against Britain. Seán Russell traveled to Germany in 1940 to canvass for arms. He became ill and died on board a German U-boat which was bringing him back to Ireland in August that year along with Frank Ryan (see Operation Dove). Stephen Hayes, the acting Chief of Staff, prepared an invasion plan for Northern Ireland and sent it to German Intelligence in 1940; this plan was later called Plan Kathleen, but it was discovered by the Irish authorities within one month of its creation. The Irish Free State opposed the IRA's collaboration with Nazi Germany, having adopted a position of neutrality.

Gunther Schuetz, a member of the Abwehr (German military intelligence), parachuted into Ireland and was almost immediately arrested. On 28 February 1942 he escaped. The IRA intended to send him back to Germany with a request for weapons, ammunition, explosives, radio equipment and money.[13] The IRA Army Executive met on 20 April and sanctioned the request. They also approved a plan to "give military information to powers at war with England even before any definite contacts [were] established with these powers", provided the information did not endanger civilians.[14] The plan was quickly discovered when an IRA courier was arrested on the Dublin-Belfast train with documentation of the decisions taken, and details of the Nazi contact. This led to the arrest of Schuetz, on 30 April, only hours before he was due to set sail. The boat was seized and the crew arrested.[15]

In 1942, the IRA launched an armed campaign in Northern Ireland. It has been rumoured[by whom?] that during the war period IRA members may have attempted to provide intelligence to assist the German aerial bombing of industrial targets in Northern Ireland. However, information recovered from Germany after the war showed that the planning of raids such as the Belfast Blitz was based exclusively on the aerial reconnaissance of the Luftwaffe.

The IRA was severely damaged by the measures taken against it by the governments on both sides of the border during the Second World War. IRA members were interned both north and south of the border, and a number of IRA men, including the chief of staff between 1942 and 1944, Charlie Kerins, were executed by the Irish government for criminal offences committed during the war. Kerins had been tried and found guilty of the murder of a local police officer (Garda).

Under the leadership of Tony Magan from 1948 on, the IRA rebuilt its organisation. In the 1950s it started planning for a renewed armed campaign, and in 1956 recent recruit Seán Cronin, who had considerable military experience, drew up a plan codenamed Operation Harvest.

The border campaign, as it became known, involved various military columns carrying out a range of military operations, from direct attacks on security installations to disruptive actions against infrastructure. The campaign received, initially, significant support from the south. Support increased massively after the deaths of Seán South and Fergal O'Hanlon in the Brookeborough Raid.[16] In the Dáil Éireann elections held in 1957, Sinn Féin fielded candidates and won four seats.

However internment without trial, introduced first in Northern Ireland and then in the Republic of Ireland, curtailed IRA operations and ultimately broke morale. Eighteen people in total were killed during the campaign, of whom seven were members of the RUC and eight were members of the IRA itself. The campaign was on the whole a failure. It petered out in the late 1950s, and was officially ended in February 1962.

In the 1960s the IRA once more came under the influence of left-wing thinkers, especially those such as C. Desmond Greaves and Roy Johnston active in the Connolly Association.[17] This move to a class-based political outlook and the consequent rejection of any stance that could be seen as sectarian—including the use of IRA arms to defend one side, that side being the beleaguered Catholic communities of Belfast in the Northern Ireland riots of August 1969—was to be one of the factors in the 1969 split that led to the Provisional IRA wing of the republican movement, with the latter subscribing to a traditional Catholic/nationalist analysis of the situation while the Officials subscribed to the Marxist view that internal strife among the working classes served only the interest of capital.[18] The Irish Department of Justice had noticed the tensions in March 1969 and advised the Dublin government to use them to fragment the IRA.[19]

The Provisional IRA embarked on a thirty-year armed campaign against the British presence in Northern Ireland that claimed 1,707 lives.[20] In 1997 it announced a ceasefire which effectively marked the end of its campaign. In 2005 it formally announced the end of its campaign and destroyed much of its weaponry under international supervision. The movement's political wing, Sinn Féin, is a growing electoral force in both Northern Ireland and the Republic.

The Official IRA mounted their own armed campaign in the Troubles up to 1972, when they called a ceasefire.[citation needed] However, some members engaged in some armed activities until 1979[21] when a decision was made to re-orient the group towards fundraising.[19]

Macardle, Dorothy (1968). The Irish Republic: a documented chronicle of the Anglo-Irish conflict and the partitioning of Ireland, with a detailed account of the period 1916-1923. Corgi. ISBN055207862X. OCLC38308.